This application is based on applications Nos. H11-155991 and H11-266452 filed in Japan on Jun. 3, 1999 and Sep. 21, 1999, respectively, the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a display optical apparatus for projecting an image formed on a reflection-type display panel.
2. Description of the Prior Art
One of conventional means of displaying an image is a projection-type display optical apparatus. Today, in a display optical apparatus of this type, a so-called reflection-type display panel such as a reflection-type liquid crystal display panel is employed. In addition, an illumination optical system is employed to illuminate efficiently and uniformly an optical image displayed on such a reflection-type display panel. Moreover, a microlens array or the like is disposed immediately in front of the reflection-type display panel to direct the illumination light emitted from the illumination optical system to the reflection-type display panel.
For example, in a so-called single-panel construction, a reflection-type display panel is used that has R, G, and B pixels arranged in a recurring pattern. Illumination light is separated into R, G, and B light beforehand, and the thus separated R, G, and B light is directed at different angles into individual microlenses of a microlens array, separately for each pixel group (here, a pixel group denotes a set of three different, i.e. R, G, and B, pixels) or for every predetermined number of pixel groups, so that the R, G, and B light is condensed individually onto the R, G, and B pixels of the reflection-type display panel.
FIG. 22 is a diagram schematically showing a conventional example of the relationship between a microlens array and a display panel. This arrangement is adopted in a single-panel-type projector optical system that employs as its display panel a transmission-type liquid crystal display panel, such as the one disclosed in U.S. Pat. No. 5,161,042. Here, where a single-panel construction is adopted, a display panel 16 is used that has R, G, and B pixels arranged in a recurring pattern. The light 9 from a light source 1 (described later) is separated into R, G, and B light beforehand, and the thus separated R, G, and B light is directed at different angles into individual microlenses 61a of a microlens array 61, separately for each pixel group, so that the R, G, and B light is condensed individually onto the R, G, and B pixels of the display panel 16. This helps achieve efficient illumination. It is to be noted that this figure shows only parts of the microlens array 61 and the display panel 16, i.e. the remaining parts thereof extending further rightward and leftward are omitted.
FIG. 23 is a diagram schematically showing another example of the relationship between a microlens array and a display panel disclosed in Japanese Patent Application Laid-Open No. H9-318904. Here, as shown in the figure, for each of the microlenses 62a of a microlens array 62, the light 9 from a light source 1 is separated not simply into R, G, and B light but into light beams corresponding to a plurality of pixel groups, arranged in the order RGBRGB . . . , before being shone thereon, so that the thus separated light beams are condensed individually onto the R, G, and B pixels of the display panel 16. It is to be noted that this figure shows only parts of the microlens array 62 and the display panel 16, i.e. the remaining parts thereof extending further rightward and leftward are omitted.
Even in a single-panel construction employing a display panel having R, G, and B pixels arranged in a recurring pattern as described above, it is desirable to achieve color display with resolution equivalent to that achieved in a so-called three-panel construction without increasing the total number of pixels. To achieve this, it is customary to adopt so-called color pixel time division whereby one screen is displayed in three cycles, with R, G, and B light focused in slightly shifted positions in each cycle, that are chronologically superimposed on one another.
However, in the arrangement shown in FIG. 22 as a conventional example, since a modern liquid crystal display panel used as the display panel there typically has a fine pixel pitch, it is not possible to achieve efficient illumination without making the distance from the microlenses 61a to the individual pixels of the display panel 16 extremely short. This makes it practically impossible to adopt this arrangement. Specifically, to obtain sufficiently high resolution, a modern liquid crystal display panel has a pixel pitch in the range from 10 to 20 xcexcm.
Where, as with the microlens array 61 of this conventional example, each pixel of the display panel 16 is illuminated with three light beams, i.e. one for each of R, G, and B light, the distance from the microlenses 61a to the individual pixels of the display panel 16 needs to be less than 100 xcexcm, and this makes it practically impossible to produce them; even if it is possible to produce them, the microlenses then have so sharp a curvature that it is impossible to achieve proper illumination because of aberrations and the like.
These problems can be effectively overcome by the arrangement shown in FIG. 23 as another conventional example. However, in this arrangement, the intervals between the light beams separated according to color are determined beforehand by a single-stage integrator realized by the use of a lens array (not shown here). Therefore, to achieve uniform illumination over a comparatively long span, as from the center to the edge of the screen, the lens array needs to be divided considerably finely; for example, even along the longer sides thereof, along which it is divided more roughly, it needs-to be divided into 4 to 7 sections or more. Thus, in this arrangement, as opposed to the arrangement described previously, the microlenses 62a need to be located far away from the individual pixels of the display panel 16. This makes the f/number of the individual microlenses 62a darker than the diffraction limit, and thus the microlenses 62a do not condense light properly.
Specifically, when the light 9 from the light source 1 is divided beforehand finely into light beams arranged in the order RGBRGB . . . by means of an integrator realized by the use of a lens array, whereas the distance from the microlenses 62a to the individual pixels of the display panel 16 is long, i.e. in the range from 500 to 800 xcexcm, the f/number of the individual microlenses 62a is darker than f/20, and thus the amount of diffraction-induced blurring (1.22xc3x97the wavelength xcexxc3x97the f/number) occurring in the image formed is of the order of 10 to 20 xcexcm, i.e. falls within the same range as the pixel pitch. As a result, practically, the finely divide R, G, and B light beams strike outside the individual pixels on the pixel surface. This degrades color purity and greatly reduces illumination efficiency.
Moreover, in general, placing a microlens array having microlenses arranged one for each pixel group immediately in front of a display panel makes the f/number of the microlenses dark, and thus causes more light to be diffracted so as to contribute to the blurring of the image formed than is focused on the pixels to form the image. Thus, this leads to rather inefficient illumination. On the other hand, with a microlens array having microlenses arranged one for every predetermined number of pixel groups (most of the embodiments described in Japanese Patent Application Laid-Open No. H9-318904 mentioned above are of this type), different light-source images are formed on nearby pixel groups, and thus the differences in brightness between different light-source images cause uneven illumination over a comparatively short span, as between adjacent pixel groups.
An object of the present invention is to provide a high-resolution display optical apparatus that achieves efficient illumination even with a display panel having a fine pixel pitch.
To achieve the above object, according to the present invention, a display optical apparatus is provided with an illumination optical system, including a color separator, for emitting, as illumination light, light polarized uniformly in a predetermined polarization direction after separating it by the color separator in such a way that light components of different wavelength ranges travel in different directions; a light modulating device having a display surface on which an optical image to be illuminated with the illumination light is displayed, and having, on the display surface, pixels corresponding to three primary colors, namely R, G, and B, arranged in a recurring pattern; a projection optical system for focusing projection light exiting from the light modulating device on an image plane; and pixel shifting means for shifting the projection light focused on the image plane by a predetermined number of pixels at a time. Here, the illumination light is composed of light beams of three primary colors, namely R, G, and B, arranged in a recurring pattern, and light beams of identical colors illuminate a plurality of adjacent pixels of corresponding colors on the display surface of the light modulating device.